Crystal Growth and Structure Determination of Oxygen-Deficient Sr₆Co₅O₁₅

Abstract

Large single crystals of oxygen-deficient Sr6Co5O(15-delta) compounds, i.e., Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36, were obtained by using K2CO3 flux in the presence of additives of transition metal oxides. The single-crystal structure determination shows that the structures of Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36 crystallize in the space group R and can be described as one-dimensional face-sharing CoO3 polyhedral chains and Sr cation chains. Unlike the other known 2H-perovskite-related oxides in which the polyhedral chains consist of octahedra (Oh) and trigonal prism (TP), the structure of Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36 contain Oh and intermediate polyhedra (IP) and can be attributed to a general structure formula A6A'2B3O(15-delta), which is closely related to the known A6A'B4O15 phases by shifting of a B atom and the O3 triangle along the c axis. Further study on O3 reveals that this oxygen position splits into two independent positions, corresponding to polyhedral geometry of IP and TP, respectively. Therefore, the polyhedral chain in the structure should be more precisely described as a random composite of the 4Oh + TP and 3Oh + 2IP. This model is used to interpret the magnetic properties, although not quantitatively. The 4-D structure analysis was also conducted for both Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36 with a commensurate modulated structure in a 4-D superspace group, R3m(00gamma)0s, gamma = p/k = 3/5. By considering the same 4-D superspace group R3m(00gamma)0s but different t-phases, one can understand the structure relationship between Sr6Co5O14.70 and Sr6Rh5O15.

Crystal structure of an oxygen deficient strontium cobaltate, Sr6Co5O14.3

“…16) Sun et al has grown single crystals of Sr6Co5O14.70 (a = 9.459(1) Å and c = 12.469(2) Å) and Ni-doped Sr6Co4.9Ni0.1O14.36 (a = 9.4401(11) Å and c = 12.476(3) Å) by a flux method. 17) They analyzed the crystal structures of these compounds using a structural model of the rhombohedral space group R3 -. 17) In this model, oxygen defects are preferentially formed at one crystallographic O site around z = 0.5 (shown with small black spheres in Fig.…”

“…17) They analyzed the crystal structures of these compounds using a structural model of the rhombohedral space group R3 -. 17) In this model, oxygen defects are preferentially formed at one crystallographic O site around z = 0.5 (shown with small black spheres in Fig. 1(b)).…”

“…Sun et al also proposed another structural model of Sr6Co5O14.70 where they further split the oxygen defect site into two sites in the same space group R3 -. 17) In this split-site model, the twelve positions of oxygen atoms with defects are introduced, and a sequence of 4Oh + 1TP arrays in addition to that of the 3Oh + 2IP arrays is statistically formed.…”

Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3

“…Several interesting magnetic properties have been reported, such as complex magnetism in Sr 3 M M O 6 (M = Ni, Cu, Zn, M = Pt, Ir) [1,2], random spin-chain paramagnetism in Sr 3 CuPt 0.5 Ir 0.5 O 6 [3] and low-dimensional magnetism in Sr 6 Co 5 O 15 [4]. These intriguing magnetic properties seem to be related to the crystal structure through atomic coordination, orbital overlap, ionic valence, crystal field and spin configurations of the magnetic ions.…”

“…The polyhedral chains are well separated by the A cation arrays running parallel to the chains. This 3D formalism (A 3n+3m A n B 3m+n O 9m+6n ) can well describe typical hexagonal compounds such as Sr 4 IrO 6 [7] or Ca 3 Co 2 O 6 [8]. However, it is inappropriate to describe all the structures within the hexagonal perovskite system.…”